This invention relates generally to safety valves for relieving pressure above a predetermined value. More particularly, but not by way of limitation, this invention relates to an improved safety relief valve including an orifice forming member that permits rapid valve opening at low pressures above the preset opening value, stability of the valve when open, and permits rapid closure of the valve as the pressure drops toward the preset opening value.
In the design of safety relief valves, it is highly desirable to provide a valve wherein the valve cracks at the preset pressure and moves rapidly at low pressure increases to the full opening position of the valve, is stable at such positions, and one that will snap closed as the pressure in the valve drops. It is also highly desirable to provide a valve wherein the flow area therethrough is such that the movement of the valve member away from the seat can be as small as possible to avoid early fatigue of the spring which moves the valve member toward the seat. Difficulty has also been encountered when the valve member is off of the seat due to an unstable condition which is frequently referred to as "chatter". Such "chatter" can cause early destruction of the valve seat preventing the complete closure of the valve.
One attempt to alleviate such problems is illustrated in U.S. Pat. No. 4,130,130 issued Dec. 19, 1978 to Robert D. Stewart et al. In that valve, there is provided an adjustable annular member that encircles an annular valve seat. The adjustable annular member or ring cooperates with a flange on a valve member carrier to form an orifice which controls the rate of opening and of closing of the valve. It can be seen in the patent that the diameter of the ring is relatively small where the orifice is formed and thus a relatively large force and relatively large lift is required on the valve to provide opening and full flow. Such an arrangement will provide stability and rapid closure of the valve when the pressure in the inlet decreases, but has the disadvantages mentioned above.